Grout Calculator

It depends on tile size and joint width. A 12x12 in tile with a 1/4 in joint covers roughly 175 sq ft per 10 lb bag (sanded), so a 100 sq ft floor needs about 0.6 bags before waste. A 1x1 in mosaic with a 1/16 in joint drops to 100 sq ft per bag because the linear feet of joint per square foot is much higher. The calculator pulls coverage from a manufacturer reference chart (Custom Building Products, Mapei, and Laticrete all publish very similar numbers) and scales for any joint width you pick.

The rule is simple: sanded grout for joints 1/8 in or wider, unsanded for joints under 1/8 in. The sand in sanded grout keeps wide joints from shrink-cracking as the cement cures. Unsanded grout is a smoother paste that packs into narrow joints (mosaic tile, polished marble, glass tile) without scratching the tile face. The calculator flags a warning if your chosen type does not match the recommendation for your joint width.

Epoxy grout costs three to four times as much as cement-based grout and is harder to work with (faster pot life, more aggressive cleanup), but it is non-porous, stain-proof, and chemical-resistant. Use it in wet areas (shower floors, steam rooms), commercial kitchens, restaurant floors, or anywhere a porous cement grout would absorb oil, wine, or grease. The calculator honors epoxy as a deliberate choice and never warns against it for joint-width reasons.

Ten percent covers the typical losses on a residential tile job: the partial bag you mix up and do not fully use, the cleanup material that goes into the bucket of rinse water, and the extra you slap into deep joints. Step up to 15 to 20 percent for very small jobs (where a single partial bag is a larger fraction of the total), for installers new to grouting, or for tile with deeper-than-spec joints. Drop back toward 5 percent for big commercial jobs where you can portion bags more precisely.

Linearly. A 1/4 in joint takes twice as much grout per linear foot as a 1/8 in joint, so coverage per bag drops in half. The calculator anchors each tile size to the joint width its published reference number is measured at (12x12 at 1/4 in, 24x24 at 1/8 in, and so on) and then scales: if you pick a wider joint than the reference, coverage drops; if you pick a narrower joint, coverage rises. That keeps the bag count honest when you deviate from the standard joint width for a given tile size.